Method of forming a gate oxide film for a high voltage region of a flash memory device

ABSTRACT

A method of forming a gate oxide film for high voltage region of semiconductor devices includes forming patterns on a semiconductor substrate having a high voltage region, thereby exposing only a gate oxide film formation region for high voltage, forming a metal oxidization layer on the entire surface, and performing a process of removing the patterns, thereby forming the metal oxidization layer only in the gate oxide film formation region for high voltage.

BACKGROUND

1. Technical Field

A method of forming a gate oxide film for high voltage region of a flash memory device is disclosed.

2. Discussion of the Related Art

A flash memory device includes a cell region having a cell transistor for storing and erasing data by way of tunneling, and a peripheral circuit unit for driving the cell transistor. The peripheral circuit unit is divided into a low voltage region having a low voltage transistor for applying a low voltage, a high voltage region having a high voltage transistor having resistance against a high voltage of about 20V, which is necessary for tunneling, and the like.

A gate oxide film for high voltage and a gate oxide film for low voltage of a predetermined thickness are formed in each of the regions. When forming the gate oxide film for high voltage, which is thicker than the gate oxide film for low voltage, there is a problem in that a “bird's beak phenomenon” is easily generated.

SUMMARY OF THE DISCLOSURE

Accordingly, in view of the above problems, a method of forming a gate oxide film for a high voltage region in semiconductor devices is disclosed wherein the thicknesses of the gate oxide films in both the high and low voltage regions are about equal, thereby avoiding a bird's beak phenomenon, which is generated when forming a gate oxide film for a high voltage region which is thicker than a gate oxide film for a low voltage region.

A disclosed method of forming a gate oxide film for a high voltage region comprises forming patterns on a semiconductor substrate having a high voltage region, thereby exposing only a gate oxide film formation region for the high voltage region, forming a metal oxidization layer on the entire surface, and performing a process of removing the patterns, thereby forming the metal oxidization layer only on the gate oxide film formation region for the high voltage region.

The metal oxidization layer is preferably an aluminum oxide (Al₂O₃) layer.

The process of removing the patterns also removes the metal oxidization layer formed on the patterns, whereby the metal oxidization layer is formed only on the gate oxide film for the high voltage region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are cross-sectional views for explaining a disclosed method of forming a gate oxide film for a high voltage region of a semiconductor device.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Where it is described below that one film is disposed “on” an other film or a semiconductor substrate, the one film may directly contact the other film or the semiconductor substrate. Or, one or more other films may be disposed between the one film and the other film or the semiconductor substrate. Furthermore, in the drawing, the thickness and size of each layer are not to scale and may be exaggerated for convenience of explanation and clarity. Like reference numerals are used to identify the same or similar parts.

Disclosed herein is a transistor for a high voltage region in a flash memory device. The transistor has a structure of a MISFET (Metal Insulator Semiconductor Field Effect Transistor). A gate oxide film of the transistor can be formed of an aluminum oxide (Al₂O₃).

FIGS. 1 and 2 are cross-sectional views for explaining a disclosed method of forming a gate oxide film for a high voltage region in a semiconductor device.

Referring to FIG. 1, photoresist patterns PR through which a gate oxide film formation region for high voltage of a high voltage region HVR is exposed is formed on a semiconductor substrate 10 in which the high voltage region HVR, a low voltage region (not shown) and a cell region (not shown) are defined, and a transistor suitable for each region is selectively formed. The photoresist patterns PR are defined so that a region in which only a gate oxide film for a high voltage will be formed is exposed.

Referring to FIG. 2, an aluminum oxide (Al₂O₃) layer 12 is formed on the entire surface in which the photoresist patterns PR are formed.

The aluminum oxidization layer 12 is formed through the following steps: an aluminum source supply step; a first purification step; an oxygen reaction gas supply step; and a second purification step, wherein the four steps forms one cycle. In the aluminum source supply step, TMA and NH3 reaction gas being an aluminum source are supplied into a reactor at the same time for a period ranging from about 0.1 to about 3 seconds, so that an aluminum (Al) layer is adsorbed on a surface of a semiconductor substrate. The NH₃ reaction gas can be supplied at the flow rate ranging from about 10 to about 100 sccm.

In the first purification step, in order to remove an un-reacted aluminum source gas and reaction byproducts, a N₂ gas can be injected or vacuum-purified for a time period ranging from about 0.1 to about 3 seconds, and is then discharged through a discharge pump.

In the oxygen reaction gas supply step, an oxygen reaction gas is supplied into the reactor for a time period ranging from about 0.1 to about 3 seconds so that oxygen is adsorbed on the surface of the semiconductor substrate.

In the second purification step, in order to purge un-reacted oxygen reaction gas and reaction byproducts, a N₂ gas can be injected or vacuum-purified for a time period ranging from about 0.1 to about 3 seconds, and is then discharged through a discharge pump.

In order to form the aluminum oxide film to a desired thickness, the four steps are repeatedly performed until a desired thickness is formed with the four steps being one cycle.

At this time, the aluminum oxidization layer 12 is formed on the photoresist patterns PR as well as the exposed gate oxide film formation region for high voltage.

Thereafter, a process of removing the photoresist patterns PR from the result in which the aluminum oxidization layer 12 is formed is performed, thereby completing the present process.

At this time, in the process of removing the photoresist patterns, the aluminum oxidization layer 12 formed on the photoresist patterns is also removed, whereby the aluminum oxidization layer 12 remains only in the gate oxide film formation region for the high voltage region HVR. The aluminum oxidization layer 12 formed as such is used as a gate oxide film for a transistor or flash memory.

Though not shown in the drawings, a process of forming a gate electrode for the high voltage region on the entire surface in which the gate oxide film for the high voltage region is formed is performed.

As described above, a gate oxide film for a high voltage region is formed only in a region in which an aluminum oxidization layer will be defined through photoresist patterns. Accordingly, a bird's beak phenomenon, which is generated when forming a gate oxide film for a high voltage region, which is thicker than a gate oxide film for a low voltage region, can be prevented. As such, since a bird's beak phenomenon, which is generated in a gate oxide film formation process for high voltage, is prevented, there are effects in that a gate oxide film formation area for high voltage can be minimized and a gate electrode topology can be minimized.

Although the foregoing description has been made with reference to the preferred embodiments, it is to be understood that changes and modifications may be made by the ordinary skilled in the art without departing from the spirit and scope of this disclosure and the appended claims. 

1-3. (canceled)
 4. A transistor for high voltage in a flash memory device, the transistor having a structure of a metal insulator semiconductor field effect transistor (MISFET), the transistor having a gate oxide film formed using a method comprising the steps of: forming patterns on a semiconductor substrate having a high voltage region, thereby exposing only a gate oxide film formation region for the high voltage region; forming a metal oxidization layer on the entire surface; and performing a process of removing the patterns, thereby leaving the metal oxidization layer only in the gate oxide film formation region for the high voltage region.
 5. The transistor of claim 4, wherein the gate oxide film of the MISFET is formed of an aluminum oxide (Al₂O₃). 